The present invention provides a method and apparatus for improved mixing in fluids, and in particular provides a method and apparatus for improved mixing in systems that use ultraviolet (UV) radiation for disinfection of fluids.
The use of ultraviolet (UV) radiation to kill microorganisms in air or fluid systems is well known. However, traditional UV disinfection systems are not very efficient in energy utilization. Up to twice as much power is used than is theoretically necessary because the UV light is absorbed by the fluid after penetrating only a short distance (less than 1 inch in water, for example), with the result that fluid that does not come close to the lamp is not treated. This invention proposes a method for creating large scale sustained mixing down the length of the UV lamp to bring substantially the entire volume of fluid close to the lamp for uniform treatment.
Traditional arrayed low pressure/low lamp power UV disinfection systems have relatively long fluid residence times within the mixing apparatus and UV lamps of a length in the direction of fluid flow that permit sufficient mixing to be achieved to result in a low energy utilization efficiency. With the introduction of medium pressure/high power lamp systems, both the fluid residence time and the length of the lamps are decreased while the spacing perpendicular to fluid flow between adjacent arrayed lamps is increased with the result that the energy utilization efficiency is reduced even further. It has been shown that mixing baffles can improve the energy utilization efficiency. However the mixing eddies created by the baffles are short lived and require high energy input (pressure drop). Waste water disinfection systems are usually gravity fed systems that do not have large amounts of head (pressure) that can be used for mixing. The need to efficiently convert flow energy into vortices which effectively mix the fluid being treated arises because in most sewage treatment plants there is little flow energy (i.e. pressure drop) to spare. Plants are built with specific pressure drop requirements in mind. In a retrofit application, one may have a pressure drop of less than six inches of water to accomplish the required mixing.
To eliminate the undesirable tradeoff between energy efficiency and energy input, the present invention proposes a set of vortices essentially axially aligned in the direction of fluid flow that sustain themselves over the length that the fluid flow is exposed to the UV lamps, with the result that the production of short-lived small scale eddies which are a waste of input energy is minimized. These vortices can be produced by several means including the use of moving or stationary structures placed in the flow path such as specially shaped baffles, propellers and contoured flow tubes, among others.
The preferred embodiment of the present invention proposes the use of matched pairs of delta-shaped wings at the inlet end of an arrayed reactor to produce the counter-rotating vortices. Through use of delta wings to create co-rotating or counter-rotating vortices, the present invention permits efficient mixing with low pressure drop to allow for more efficient use of the UV light in stimulating heat and/or mass transfer in the chemical reactions causing fluid disinfection to consequently reduce the capital and operating costs of UV disinfection systems.
Accordingly, it is an object of the present invention to provide a method and apparatus to achieve increased mixing within arrayed or non-arrayed fluid flow systems so as to increase the energy utilization efficiency in such systems without degrading system energy input requirements.
It is a further object of the present invention to provide a method and apparatus to achieve increased mixing in arrayed or non-arrayed fluid flow systems by creating a set of co-rotating or counter-rotating vortices that sustain themselves throughout the entire duration of fluid travel through such systems.
It is a further object of the present invention to use delta-shaped wings at the inlet end of an arrayed or non-arrayed fluid flow system to produce co-rotating or counter-rotating vortices for the purpose of achieving increased mixing in such systems.
Accordingly, it is an object of the present invention to provide a method and apparatus to achieve increased mixing within ultraviolet (UV) fluid disinfection systems to increase the energy utilization efficiency in such systems without degrading system energy input requirements.
It is a further object of the present invention to provide a method and apparatus to create a set of co-rotating or counter-rotating vortices in UV fluid disinfection systems that sustain themselves substantially throughout the entire duration of fluid exposure to UV radiation.
It is a further object of the present invention to use delta-shaped wings at the inlet end of a UV fluid disinfection system to produce co-rotating or counter-rotating vortices for the purpose of achieving increased mixing in such systems.
Although the present invention is described in particularity as embodied in a UV disinfection system, it will be understood by those skilled in the art that the present invention has equal applicability to other types of arrayed or non-arrayed flow systems in which increased fluid mixing is desired.
The preferred embodiment of the present invention provides an apparatus and method for accomplishing fluid mixing by passing fluid flow through an array of ultraviolet lamps lying essentially along the direction of fluid flow that define channels for the fluid flow. Positioned upstream or adjacent to each tube are triangular shaped delta wings having surfaces inclined at an angle to the direction of fluid flow. The interaction of the fluid flow with each delta wing creates a pair of vortices that counter-rotate in opposite directions to each other. These counter-rotating vortices reinforce each other to minimize dissipation of their mixing strength as they move down the channel. Due to these co-reinforcing properties, the counter-rotating vortices promote more efficient mixing of the fluid to achieve more efficient use of the light in the UV disinfection system.
Although the present invention is described in particularity as embodied in a UV disinfection system, it will be understood by those skilled in the art that the present invention has equal applicability to other types of arrayed or non-arrayed flow systems in which increased fluid mixing is desired, and that self-sustaining co-rotating or counter-rotating vortices axially aligned in the direction of fluid flow can be produced by several means other than delta wings, including the use of moving or stationary structures placed in the flow path such as specially shaped baffles, propellers and contoured flow tubes, among others.
Other details, objects, and advantages of the present invention will become apparent in the following description of the presently preferred embodiments.